In an image-forming device such as a laser printer, an electrostatic latent image is formed on a photosensitive drum, and developer is supplied from a developer cartridge to the latent image, thereby a developer image is carried on the surface of the photosensitive drum. Subsequently, the developer image is transferred onto a sheet of paper, forming an image on the paper.
The developer cartridge is commonly configured of a casing for accommodating developer, a developing roller rotatably supported in the casing for carrying developer within the casing, and a thickness-regulating blade for regulating a layer thickness of developer carried on the developer roller. The casing also has an elongated opening formed therein. The developing roller is disposed so that a portion of the roller is exposed through the opening to confront the surface of a photosensitive drum disposed in the image-forming device. The thickness-regulating blade is a thin plate extending in an axial direction of the developer roller and has the upper end portion supported by the casing and the lower end portion pressed against the surface of the developer roller. As the developing roller rotates, the developer accommodated in the casing is supplied to the surface of the developer roller, passes between the thickness-regulating blade and the surface of the developing roller, thereby maintaining a uniform thickness of developer on the surface of the developing roller. When the developer carried on the surface of the developing roller comes into contact with the surface of the photosensitive drum, the developer is attracted to an electrostatic latent image formed on the surface of the photosensitive drum in order to develop the image into a developer image.
This type of developer cartridge has been conventionally provided with a plurality of sealing members individually disposed around the opening to prevent developer from leaking through the opening. A printer disclosed in the Japanese Patent Application Publication No. 2001-60040 is provided with side seals disposed between each end of the developing roller and the casing to prevent developer from leaking therethrough. The printer is also provided with an upper seal disposed between the thickness-regulating blade and the casing to prevent developer from leaking therethrough.